1. Field of the Invention
This invention relates to a process for decomposing gaseous iron pentacarbonyl into solid iron and gaseous carbon monoxide. More specifically, this invention relates to a process for decomposing gaseous iron pentacarbonyl involving the step of contacting the pentacarbonyl with a homogeneous gaseous catalyst.
2. Description of the Prior Art
When iron pentacarbonyl is decomposed into free iron and carbon monoxide, the resulting iron is of very high purity. Because of the high purity, the iron is in demand for use wherever very pure iron is needed.
The fact that iron pentacarbonyl can be decomposed into iron and carbon monoxide is taught in U.S. Pat. No. 1,789,813 which issued to Wilhelm Gaus in 1931. Gaus removes iron from ores by reducing the iron oxide present in the ore to iron with hydrogen or the like, reacting the iron with carbon monoxide at high temperatures and under high pressures to form iron pentacarbonyl and then decomposing the pentacarbonyl by subjecting it to a temperature of about 200.degree. C or more.
U.S. Pat. No. 3,767,378 which issued to Andrew A. Cochran et al. in 1973 indicates that reduced pressure used alone or in combination with temperatures of from about 280.degree. to about 350.degree. C will bring about decomposition of iron pentacarbonyl. More specifically, Cochran et al. describe a process whereby an ore which contains iron oxide is subjected to a reducing agent such as hydrogen to reduce the oxide to iron, the iron is treated with carbon monoxide in the presence of ammonium sulfide to produce iron pentacarbonyl and the iron pentacarbonyl is decomposed to iron and carbon monoxide by means of reduced pressure alone or in combination with heat. The ammonium sulfide acts as a catalyst to speed the reaction of the iron and carbon monoxide to form iron pentacarbonyl.
In addition to disclosing the usefulness of ammonium sulfide as a catalyst in the formation of iron pentacarbonyl, Cochran et al. discuss experiments in which they attempted to use ammonia as a formation catalyst. They found that ammonia was helpful but not very helpful in the promotion of the formation of the carbonyl.
Despite the fact that iron pentacarbonyl will decompose into iron and carbon monoxide at the temperatures mentioned by Gaus (200.degree. C +) and Cochran et al. (280.degree. to 350.degree. C), the decomposition is rather slow. Cochran et al., for example, disclose that a "longer residence time" is desirable. In other words, in their process wherein carbon monoxide is passed over iron to form the pentacarbonyl and the pentacarbonyl is subsequently decomposed, the flow of gas in the decomposition zone must be slower than that in the formation zone. Since it is desirable to recycle the carbon monoxide produced during the decomposition stage, it would be advantageous if the decomposition state could be speeded up. That is, it would be advantageous if decomposition could be made to occur at about the same rate as formation.